PLASTIC 

 LINDER 



STUFFING 

 TUBE 



EPOXY 

 FILLING 



COLLAR 



RESISTORS 



FIBER 

 SPACERS 



•GUARD 



THERMAL 



LAG 

 COATING 



Fig. 3- Thermistor assembly. 



Corporation) which is the bead type with a glass 

 probe covering. They are 2 inches in length, 

 have adjacent leads and have a nominal resistance 

 of 2,000 ohms at 25°C. 



The construction of the thermistor assembly is 

 shown in Fig. 3- The thermal time constant of 

 the thermistor thus encapsulated was approximately 

 0.5 second. Since the temperature readings were 

 to be taken at intervals of from 10 seconds to 

 1 minute, "aliasing" of the temperature signal 

 could occur unless a thermal lag was introduced. 

 For this reason, the thermal time constant was 

 increased to about 16 seconds by applying several 

 coats of an epoxy resin. 



surface and in usual operation is attenuated 

 below the system detection level. Wear the sur- 

 face these fluctuating components would have to 

 be filtered out to prevent aliasing when the 

 pressure reading is sampled at intervals equal to 

 or longer than one-half the period of surface 

 waves present. 



A Statham Laboratories, Inc. Model PA208TC 

 unbonded strain gage pressure transducer was used. 

 This was an absolute gage with a range of 0-500 

 psia and a combined nonlinearity and hysteresis 

 of less than ±0.75$ of full scale. 



MONITOR AMD RECORDING SYSTEMS 



PRESSURE INDICATING SYSTEM 



It was necessary to record depth variations 

 concurrently with the temperature records for 

 subsequent compensation during analysis. Since 

 the depth desired was that of the temperature 

 sensors, the ideal location of the pressure 

 transducer inside the hull would be directly 

 under the strut or tower containing the tempera- 

 ture sensors. The transducer was simply con- 

 nected to the nearest sea chest by means of a 

 high pressure line within the hull. The pres- 

 sure at the sea chest has a quasi-static com- 

 ponent and a fluctuating component due to the 

 surface wave action. The latter pressure drops 

 off exponentially with distance from the free 



The main purpose of this paper is to describe 

 the transducers so the following discussion of 

 recording techniques is limited to features that 

 are pertinent to transducer design or operation. 

 An independent and relatively simple visual moni- 

 tor and data recording system (Fig. k) employs 

 strip chart recorders to handle temperatures from 

 5 thermally lagged thermistors, a single pressure 

 transducer and the relatively fast temperature 

 fluctuations of one uncoated thermistor. All 

 data analysis is done on a CDC l6ok (Control Data 

 Corporation) digital computer. A block diagram 

 of the digital data recording system designed to 

 match the CDC l6o4 is shown in Fig. 5- The 

 bridges were built at USNEL; the associated digi- 

 tal system was built according to our specifications 



51 



